Almost nothing is known about hyperactive and/or learning disabled girls, for most researchers have either studied males exclusively or else lumped the few affected girls with their more numerous male counterparts. Yet there is ample evidence from which to infer critical sex differences within both clinical groups. This proposal aims (1) at answering the practical question of whether experimenters can justifiably combine hyperactive and/or learning disabled boys and girls and (2) at shedding light on the theoretical issue of whether the basic causes of the two disorders are different in males and females. Subjects will be 10 hyperactive girls without reading deficits, 10 hyperactive girls with reading deficits, 10 reading disabled girls who are not hyperactive, and 10 normally behaved and achieving girls. All girls will be aged 7 to 10 years and have WISC-R IQs of 95 or above. Results will be contrasted with those obtained from similar groups of males previously studied in our laboratory. Measures to be employed include teacher and parent rating forms, tests of cognitive style, and the Children's Personality Questionnaire. Additionally, the concepts of "strength" of the nervous system and augmentation-reduction will be studied via reaction time to tones of increasing intensity given under three conditions: baseline, high gain, and low-gain (frustration). Of concern will be speed of response to soft as opposed to loud tones, practice and fatigue effects, effects of a weak stimulus on a subsequent strong stimulus and the converse, and effects of reinforcement and frustrative non-reward. Differences between sexes and clinical groups would dictate different remedial and therapeutic efforts, especially with regard to use of psychostimulants.